Geologic Time Scientists have developed a model of the history of life on Earth called the geologic time scale. Paleontologists divide the geologic time scale into blocks of time called eras and periods.

Precambrian era The Precambrian era lasted from Earth’s formation until 542 million years ago (mya). 90% of Earth’s History The first cells appeared at the end of Precambrian era.

Paleozoic era The Paleozoic era lasted from 542 to 251 mya. Paleozoic is a Greek word meaning “ancient life.” First Fish First Trilobites Seedless Land Plants were common Forests covered land

Mesozoic era The Mesozoic era lasted from 251 to 65 mya. This era is often called the Age of Reptiles. First birds. First Flowering Plants First Dinosaurs Mesozoic means “Middle Life”

Cenozoic era The Cenozoic era began 65 mya and is still going on. Fossils from the Cenozoic era are closest to Earth’s surface, making them easier to find. The Cenozoic Era is often called the Age of Mammals because mammals diversified into a variety of species including land mammals, sea mammals, and flying mammals. Cenozoic means “Recent Life”

Answer these 3 questions on a separate sheet of paper. 1. What is the order of the four major eras? 2. Write a short article explaining Earth’s History by describing each of the eras. 3. Were you using relative or absolute dating when creating your timeline? Explain.